PerC homologs have been identified in a number of Gram-negative pathogens of clinical importance, including Salmonella enterica, Shigella sp., Klebsiella pneumonia, Enterobacter cloacae, and multiple E. coli serotypes and pathotypes, constituting a super family of regulatory proteins. PerC of EPEC and the PchABC proteins of EHEC are interchangeable in function, activating expression of their respective type III secretion systems, and they are more related by phylogenetic analysis than the other members of the super family. We ask for support to use biochemical and genetic approaches to elucidate the molecular mechanism of PerC control of transcriptional activity in EPEC. As the molecular mechanism of PerC is unknown, we aim to determine how PerC, a surrogate for the Pch proteins of EHEC and other related bacteria, stimulates transcription on the molecular level. Evidence to date suggests that PerC acts not by binding directly to regulatory DNA, but by some other mechanism. Thus our working hypotheses are that PerC acts either by binding to a regulatory protein, modulating DNA binding or by interacting with regulatory RNA. With an understanding of the mechanism of action of the Pch homologs we envision targeting this regulatory pathway for therapeutic intervention.